Essential hypertension is a complex clinical disorder in which multiple environmental and genetic factors interact to increase blood pressure. To search for chromosome regions that contain genes regulating blood pressure, some investigators have begun to conduct linkage studies in rodent models of spontaneous hypertension. Preliminary results suggest that in the rat, blood pressure regulatory genes may be located in the vicinity of the kallikrein gene family on chromosome 1, the gene for angiotensin converting enzyme on chromosome 10, the renin gene on chromosome 13, and the major histocompatibility complex on chromosome 20. Some studies have also suggested that blood pressure regulatory loci may be located on the sex chromosomes. Although comparisons between humans and animals should be made with caution, it is hoped that the identification of genes regulating blood pressure in the rat might shed light on the pathogenesis of hypertension in humans.